Zombies are the new Nazis in gaming. World War II is out, Zombie Apocolapse is in. They are the new thing that you can shoot and shoot and shoot without getting bored (that is, until something new comes along and replaces zombies).
Many current games now are about zombies or feature them in some way.

A zombie is either an actual undead (which is the case with Nazi Zombies), or a human who was infected with a virus of some sort and have undead/zombie like charactoristics (like Left 4 Dead).

A "safe" and offbeat excuse for guys to horde guns, ammunition, tactical gear and other survival supplies without being tagged as being a member of a militia or other extremist group (although your wife and neighbors may think you are a little crazy).

Bob: I just ordered 1000 rounds of 9mm for the two new Glocks I bought last week.

Tom: Damn Bob, are you one of them whacko militia members the government has been warning us about?

An undead soul, possessed and sent out of the grave to thrive upon the flesh of the living.

After a dead body rots underground for a time, it may come to life, first its eyes will reopen, and fingers will begin twitching. The thumping of the heart may return, unless the heart has been removed. This is the rebirth of a human, the birth of a zombie.

Deteriorating, fallen apart and reaking of the foul stench of death, a zombie will raise from the grave by smashing through the coffin and lifting an arm out of the ground, in the normal zombie style. The zombie will proceed to lift itself out of the soil and moan, usually moaning anything like 'Yaaarghhh...' or 'BRAINS!'

If you fall victim to the zombie's feasting of your flesh and brain, you will become a zombie, forever walking, undead.

Noun: (Zohm-bees)
Commonly confused as brain suckers. These originated from the religion of Voodoo. They are the dead brought back to life only in the body, while the soul is in torment. The only reason they walk the earth is to bite the living, who, once bitten also become a zombie. They are usually formed from a curse on a living person, who once dead will become one.

Zombies? This is one hell of a bad trip...
Zombie: Can I eat your spleen
Living guy: No, fuck off
Zombie: Oh... sorry.

(Noun)- to have the resemblance of a zombie. Characterized by bed head, bad breath, looking tired and/or just by looking jacked up in your appearance
(Verb) means to stay up all night; pull an all nighter.

(Noun form)- That dude went to prom looking like a straight up zombie.
(Verb form)- Haris Shekhani had to zombie it for his physics test the next day.